It depends on who you ask. Many say no. The argument goes like this: The purpose of cyanuric acid is to protect chlorine from UV light degradation. There is no UV light in an indoor pool. Therefore, cyanuric acid should not be used in an indoor pool.
The PHTA’s latest ANSI standard (APSP-11) states “Cyanuric acid is not recommended for indoor pools or spas where protection from sunlight is not necessary.”
PHTAis not alone in recommending cyanuric acid not be used in indoor applications, but some codes are even more vehement. Some say it should NEVER be used in indoor pools. In fact, some states and local codes specifically prohibit the use of CYA in indoor pools.
Why? Is it toxic? Is it carcinogenic (cancer causing)?
Studies have shown that cyanuric acid has very low toxicity. It is also not considered carcinogenic.
So why do some codes ban cyanuric acid in indoor settings?
Perhaps it does something harmful to the air in an indoor setting that a breeze cannot blow away?
Well, this is where things get interesting. The answer to that is probably no – in fact, it may do something beneficial to the air in an indoor environment.
In general, the disinfection byproducts of chlorine with batherintroduced contaminants (sweat, urine, skin cells, and lotions) are bad. Many of them cause genetic mutations or are carcinogenic. There’s a complex mixture of disinfection by-products, some of which are volatile and skin-permeable, such as trihalomethanes.
Trichloramine and other volatile chemicals in swimming pools are respiratory irritants, and pool attendance has been associated with asthma and other respiratory effects in Olympic swimmers and pool workers.
Many studies have linked asthma to volatile disinfection byproducts such as chloramines and especially trichloramine. This is further corroborated by worse health effects for those who frequent indoor swimming pools as compared to outdoors. Similarly, competitive and regular swimmers have been reported to experience higher cases of asthma and other respiratory issues than any other type of professional sports person.
Further evidence of the negative health effects of disinfection byproducts comes from a survey of lifeguards working at indoor pools, where 55% suffered from respiratory and other health issues.
Other studies have linked trihalomethane swimming exposure to bladder cancer. Collectively, these studies have associated an increased risk for bladder cancer due to dermal and inhalation exposure of certain kinds of disinfection by-products in disinfected waters But what effect does cyanuric acid have on any of this?
At this point, more studies are needed to show what effects cyanuric acid may have on the harmful volatile disinfection by-products that are formed when chlorine reacts with the water’s contaminants. Most reports have, however, indicate that cyanuric acid does decrease some of the harmful disinfection by-products that people inhale in an indoor pool.
For example, a 2016 study entitled An insight of disinfection by-product (DBP) formation by alternative disinfectants for swimming pool disinfection under tropical conditions examined the types of disinfection by-products formed with or without cyanuric acid. Researchers found that: “The result reveals that halogen stabilizer, TCCA, [Trichlor] had the advantages of slower free chlorine degradation and lower DBP [disinfection by-product] concentration compared to NaClO [liquid chlorine alone], which makes it a good alternative disinfectant.”
In other words, cyanuric acid reduces some of the harmful things that swimmers inhale in an indoor pool, and that is a good thing.
In a swimming pool, we are talking about chloroform. And for those who do not know, chloroform is a suspected carcinogen as per the International Agency for Research on Cancer (IARC) monographs.
Chloroform is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act.
Virtually all studies show a correlation between the active chlorine level and the rate of formation of disinfection by-products. In other words, these by-products form as a function of how much active chlorine is available.
So here’s the argument: Maintaining a lower active chlorine level reduces the rate of formation of the by-products. Cyanuric acid lowers the active chlorine level. Therefore, cyanuric acid helps to lower the quantities of harmful disinfection by-products.
So should you use cyanuric acid in an indoor pool?
At this point, it’s starting to seem like a good idea.